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Background: The ability to manipulate the development of pancreatic insulin-producing βcells has implications for the treatment of type 1 diabetes. Previously, we found that laminin-1, a basement membrane trimeric glycoprotein, promotes β-cell differentiation. We have investigated the mechanism of this effect, using agents that block the receptors for laminin-1, α6integrin, and α-dystroglycan (α-DG). Materials and Methods: Dissociated cells from 13.5-day postcoitum (dpc) fetal mouse pancreas were cultured for 4 days with laminin-1, with and without monoclonal antibodies and other agents known to block integrins or α-DG. Fetuses fixed in Bouin’s solution or fetal pancreas cells fixed in 4% paraformaldehyde were processed for routine histology and for immunohistology to detect hormone expression and bromodeoxyuridine (BrdU) uptake. Results: Blocking the binding of laminin-1 to α6integrin with a monoclonal antibody, GoH3, abolished cell proliferation (BrdU uptake) and doubled the number of βcells. Inhibition of molecules involved in α6integrin signaling (phosphotidylinositol 3-kinase, F-actin, or mitogen-activated protein kinase) had a similar effect. Nevertheless, βcells appeared to develop normally in α6integrin-deficient fetuses. Blocking the binding of laminin-1 to α-DG with a monoclonal antibody, IIH6, dramatically decreased the number of βcells. Heparin, also known to inhibit laminin-1 binding to α-DG, had a similar effect. In the presence of heparin, the increase in βcells in response to blocking α6integrin with GoH3 was abolished. Conclusions: These findings reveal an interplay between α6integrin and α-DG to regulate laminin-1-induced β-cell development. Laminin-1 had a dominant effect via α-DG to promote cell survival and β-cell differentiation, which was modestly inhibited by α6signaling.

Background: Insulin (1) and glutamic acid decarboxylase (GAD) (2) are both autoantigens in insulin-dependent diabetes mellitus (IDDM), but no molecular mechanism has been proposed for their association. We have identified a 13 amino acid peptide of proinsulin (amino acids 24–36) that bears marked similarity to a peptide of GAD65 (amino acids 506–518) (G. Rudy, unpublished). In order to test the hypothesis that this region of similarity is implicated in the pathogenesis of IDDM, we assayed T cell reactivity to these two peptides in subjects at risk for IDDM. Materials and Methods: Subjects at risk for IDDM were islet cell antibody (ICA)-positive, first degree relatives of people with insulin-dependent diabetes. Peripheral blood mononuclear cells from 10 pairs of at-risk and HLA-DR matched control subjects were tested in an in vitro proliferation assay. Results: Reactivity to both proinsulin and GAD peptides was significantly greater among at-risk subjects than controls (proinsulin; p< 0.008; GAD: p< 0.018). In contrast to reactivity to the GAD peptide, reactivity to the proinsulin peptide was almost entirely confined to the at-risk subjects. Conclusions: This is the first demonstration of T cell reactivity to a proinsulin-specific peptide. In addition, it is the first example of reactivity to a minimal peptide region shared between two human autoimmune disease-associated self antigens. Mimicry between these similar peptides may provide a molecular basis for the conjoint autoantigenicity of proinsulin and GAD in IDDM.